Print monitoring systems are commonly used to monitor printed matter in some types of paper/sheet handling systems and to make certain control decisions based upon the character of the printed matter. The following is a list of a few common applications:
1. Print quality monitoring: The monitoring system detects the precision with which the printing system has formed the printed matter and/or the consistency with which the matter is printed across the entire paper. For example, in a laser printing system, the monitoring systems detect a low-toner situations where the contrast of the printed matter has degraded unacceptably.
2. Digit control: Overnight package delivery systems, for example, typically use a preprinted multi-layered shipping receipt that is filled out by the customer; the customer keeps one receipt, the package recipient receives a receipt with the package, and then typically, a few receipts are retained for the carrier""s records. Such receipt systems are typically printed with a package tracking number that is represented as an alpha-numeric sequence on the customer""s and recipient""s copies and encoded in a universal product code (UPC) or bar code symbol on at least one of the carrier""s receipts. The carrier""s package tracking system is based upon the presumption that the package tracking numbers are the same for each layer of the receipt. In such situations, print monitoring systems ensure that package tracking numbers of each layer match during assembly of the receipt.
3. Sequence control: When mailing personalized advertisement materials and in all cases when mailing bills, it is necessary to ensure that all pages of the mailing insert are combined into the proper envelope. This is especially important in the case of confidential information, such as credit card or phone bills. Even if sheet transfer and handling error rates are low, the risk that a wrong bill will be sent to a customer is unacceptable thus requiring checking each page and the envelope prior to insertion.
While a number of different configurations exist, many print monitoring systems use a multi-slave processor/master processor configuration. The slave processors are used to receive image data from some type of image capturing device such as a line-scan camera or frame capture camera. The detected image is buffered by the slave processor for transmission to the master processor, which executes an optical character recognition (OCR) or one or two dimensional UPC symbol decoding algorithm.
Problems exist, however, with known print monitoring systems. Generally, they tend to be expensive to manufacture from the standpoint of part counts/components. This is especially true for the slave processor boards, which must be replicated for each image capture device. Additionally, existing systems also tend to have poor scalability. Each slave processor requires substantial attention and control from the master processor, thus restricting the number of additional slave processors that can be added onto or supported by a given master processor. This factor additionally contributes to the limited ability of these systems to compare the data received from the slave processors with other sources without overloading the ability of the master processor to manage the data in real-time.
The print monitoring system of the present invention implements a number of improvements that overcome the above-described problems with the prior art. The innovations can be classified into separate groups. First, a combination of an analog signal processing circuit and signal processor is used on the slave processing boards to avoid the need for analog-to-digital converters and dedicated frame buffers between the slave processor and the video capture device. Secondly, the division of labor between the slave processors and the master processor is configured such that the slave processors perform a larger portion of the data manipulation, data analysis for the captured images. The master processor can be simply used to collect the decoded data and/or data analysis results from the slave processors and to run the interface to the operator to communicate the data/results. Finally, a graphical user interface between the user and the master processor is used to facilitate the calibration of the system and specifically the images captured by each of the video cameras.
In general, according to one aspect, the invention features the print monitoring system for scanning and processing printing matter. The system comprises an image capturing device that generates an electrical analog video signal representative of scanned areas of the printed matter. A processor receives the analog video signal at a digital signal port and internally stores the video signals for digital signal processing. In order to enable this direct sampling, an analog preprocessing stage is utilized between the processor and the image capturing device that level adjusts the analog video signal to enable receipt at the digital signal port.
In specific embodiments, the processing stage thresholds the analog video signal prior to receipt at the digital signal port with the processor preferably setting the threshold. The preprocessing stage also comprises an illumination compensation circuit that compensates for uneven illumination of the printed matter. This functionality is achieved by low pass filtering the signal from the image capturing device, preferably using an asymmetric filter.
In the preferred embodiment, the processor is a digital signal processor and the digital signal port is its serial port. The processor preferably has an internal data memory that serves as a frame buffer for the video data from the image capturing device. In specific embodiments, the image capturing device can be a line scan camera, an array camera, asynchronous reset camera, or a progressive scan camera.
In general, according to another aspect, the invention features a print monitoring system. The system comprises at least one image capturing and processing subsystem having at least one image capturing device that generates video signals representative of printed matter and a slave processor that processes and analyzes and/or decodes the video signals. A master processor downloads image decoding and/or image analysis criteria to the slave processor in the subsystems and receives the decoded data and/or analysis data from the slave processor for presentation to an operator.
In general, according to still another aspect, the invention features a user interface for a print monitoring system. The interface displays an image captured by a camera of the system and then enables adjustment of a size and location of a decoding field within the captured image. In this way, the portion of the image in which the character recognition algorithm, for example, is used can be controlled in software, avoiding the need for manual measurements under the camera.
In general, according to still another aspect, the invention features a user interface for a print monitoring system. It displays a template character taught to the system and enables modification of the shape of the template character. In this way, model characters presented to the system either through a learning sequence or directly programmed can be modified to improve the accuracy of the character recognition algorithm.
The above and other features of the invention including various novel details of construction and combinations of parts, and other advantages, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular method and device embodying the invention are shown by way of illustration and not as a limitation of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention.